Field of the Invention
The present invention relates to methods for manufacturing photonic devices and to photonic devices manufactured by such methods. The invention has particular, but not exclusive, application to the manufacture of liquid crystal laser devices.
Related Art
Liquid crystal (LC) materials are a class of functional photonic materials. LC materials contain molecules which have a tendency to self-organize along an optical axis. The way in which the molecules in LC materials align dictates the optical properties of the LC material. For example, chiral liquid crystals have a tendency to self-organize into a helicoidal arrangement around an optical axis. Due to the birefringence of the material, this helicoidal arrangement results in a periodic variation of the refractive index along the optical axis. For suitable periodicities, this gives rise to a photonic band-gap for visible wavelengths of circularly polarized light.
The optical properties of chiral LC materials make them suitable for applications ranging from bistable displays to lasers. Incorporation of an organic laser dye, as the light harvester or gain medium, into the optical cavity can lead to laser emission at the photonic band-edges. Laser devices built based on these materials are characterised by very low cost manufacturing, small size and selectable wavelength of emission, currently in the range 400 nm to 850 nm (See References [4] and [2]).
Applications of achiral LC materials include conventional flat-panel displays (nematic LCDs), variable retarders and SLMs.
US2011/0097557 discloses the manufacture of security features, e.g. for bank notes, in which a polymerisable LC material is printed onto a solid PVA layer. The PVA layer is unrubbed but is found to promote alignment for certain LC materials.
Conventional semiconductor lasers used in most modern laser systems are solid-state devices that are typically manufactured using a complex process involving a combination of deposition, etching and photolithographic steps on high quality single crystal semiconductor wafers. Such conventional lasers cannot be manufactured using relatively low cost printing technologies such as bar coating or inkjet printing, for example. It has previously been shown in References [11] and [12] that printable emulsion-based LC laser systems can be deposited on a wide variety of substrates including, for example, glass, plastic, metal or paper. These documents describe deposition of a LC lasing medium onto suitable substrates using emulsified samples and a simple bar-coating process. In these disclosures, the liquid crystal and laser dye composition were emulsified in a continuous phase of PVA, this emulsion then being applied to the substrate. Subsequent drying of, and interfacial interaction with, the continuous phase causes advantageous stresses to be applied to the LC droplets, assisting in the development of suitable alignment of the LC molecules.